Layne is an animal lover and grew up in a household full of rescued critters. She is a registered veterinary technician.
What Causes Dog-on-Dog Aggression?
Aggression towards other dogs can happen suddenly and for a variety of reasons. It can be extremely shocking to witness when it happens the first time, especially if this is out of character for your dog. In general, dogs that have been well-socialized avoid confrontation and they communicate this via posturing and body language.
It might be overwhelming at first to consider the numerous reasons why your dog may act out aggressively or get attacked by another dog (even in the same household). We will go over these reasons below and also talk about ways you can stop the fights from happening:
Common Causes of Dog-on-Dog Aggression
- Fear or Feeling Threatened
- Pack Mentality
- Feeling Threatened by a Dog's Size
- Confinement in a Small Space
- Territoriality (Resources) and Dominance
- Protecting the Owner, Family, or Family Pet
- Excitability or Curiosity
- Barriers (Leash or Fence)
- Prey Drive
- Health Issues
12 Reasons Why Dogs Attack Other Dogs
Here are 12 common reasons why a dog might act aggressively towards another dog, person, animal, or even an inanimate object. If your dog is prone to this type of behavior, you will want to identify the issue immediately and even consider working with a certified behaviorist.
One of the most obvious reasons why a dog may be aggressive towards other dogs is from early periods of undersocialization. Behavioral specialists can’t emphasize enough the importance of socializing your dog from an early age—that means exposing them to other dogs, people, scenarios, situations, and places. What’s challenging about early socialization is your puppy’s size (your puppy can be easily injured or negatively affected if playing with dogs that are too big for its size or play style) and the risk of transmissible disease (parvovirus, especially, and everything covered by the DHPP vaccine).
In general, puppies are required to have 3 rounds of the DHPP vaccine (a core vaccine); this can occur at 6 weeks, 8 weeks, and 10 weeks (might vary depending on your veterinarian). Thereafter, the rabies vaccine will be administered at 4 months of age. (The rabies vaccine is required by the county and protects your dog from rabies that is transmissible by wildlife.) Your puppy is considered generally protected after the first two DHPP vaccines, but to be safe, you want to avoid walking them on surfaces that wildlife and adult dogs may have transversed on (parvovirus is a hardy virus that can live on surfaces for months and is often deposited in the poop).
Alternatively, you can sign your puppy up for a puppy socialization class (vaccines required, highly recommended) or socialize your dog with your neighbor’s dog or a family friend’s pet that you know very well (sweet, gentle, ect.). Bottom line: Socialize your dog early.
2. Fear or Feeling Threatened
Aggression that is caused by fear is linked to lack of socialization from an early age. It is also possible that your dog had an early negative experience. If you adopted your dog and they come from a history of abuse, they might be placed in a scenario that is triggering for them (think of dogs that were formerly used for fighting). Even the sweetest dogs can act aggressively when scared. This can happen very readily at the vet’s office, for example (sweet dogs come in and are separated from owner, and suddenly they are lunging and biting), or other public settings.
When it comes to acting aggressively towards other dogs, this is usually triggered by your dog's own insecurity or the situation. Your dog might be backed into a corner, trapped, and feel like it is being targeted. Your dog might be being chased at the dog park by larger dogs or a pack of dogs and feel a need to defend itself (fight or flight). It’s also possible that you have multiple dogs in your household and one is a bully (is too rough on your older dog) and one day your dog just decides to snap. You can help de-escalate these situations by learning to read the room. We will talk about this further dow.
In addition, a recent study suggests that dogs also release hormones, oxytocin and vasopressin, when presented with a stimulus; it was found that dogs with more oxytocin in their bloodstream tend to be less aggressive, whereas those with more vasopressin in their bloodstream exhibit aggressive behaviors. This is all rooted in stress.
3. Pack Mentality
The pack mentality can be dangerous, and you usually see this happening in dog parks or dog beaches or at doggy daycares. This is why it’s especially important to watch your dog at all times. A lot of owners like to tune out and talk to other owners in the park while their dog goes off to exhaust themselves and play. In reality, you are gambling here (whether it's your dog that attacks or gets attacked). Both scenarios can happen: Your dog can be the one being chased or your dog can do the chasing, and both can result in a dog fight.
When dogs congregate, there is often an immediate establishment of hierarchy (albeit temporary); there are top dogs (alpha) dogs, betas, and so forth. When a group of dogs get together and start chasing, they can develop a pack mentality and act uncharacteristically. This means they might start chasing a “weaker” dog or targeted dog, and when this “prey” is put in a compromising position, they may get attacked or have to attack to defend themselves from the pack.
If your dog is the type that likes to chase or is of a breed that has a high prey drive, make sure you watch them and that they don’t instigate any unfair or dangerous games of chase.
4. Feeling Threatened by a Dog's Size
This issue can go both ways—some dogs are threatened by smaller dogs (think Great Dane vs. Chihuahua) and some dogs are obviously threatened by larger dogs. A Great Dane, for instance, which tends to be slower due to sheer size, might be fearful of a small, nipping Chihuahua at its ankles. Similarly, a small Chihuahua might feel threatened by a larger dog because the Chihuahua could be easily injured and trampled on by the larger dog or breeds if they aren’t careful around them.
Always make sure your dog is comfortable with those it is surrounded by and that its playmates play fair. All breeds and mixes can get along, but you really have to be diligent as an owner to determine which companions your dog should be socializing with.
5. Confinement in a Small Space
It is not uncommon for a dog to get defensive due to fight or flight because of space issues. This is especially true of dogs that live together in the same house. If you live in a small space and there is very little territory for your dogs to have as their own (to feel safe), it is possible that a fight or attack will ensue when one feels like it is being backed into a corner, literally.
Just like how humans don’t like confinement, dogs can feel threatened and compromised by lack of space, so the only natural reaction is to defend and act out. Because dogs communicate differently from humans, this will look like aggression. We will talk about ways to work with this further down.
6. Territoriality (Resources) and Dominance
Issues around territoriality and dominance can occur in a variety of environments. It can be as simple as your dog sitting on their bed (being approached by another) and reacting aggressively, another dog in the household getting near their favorite bone or toy or trying to sit in their usual spot, another household animal approaching your dog when they are napping in their crate, and so forth.
Territoriality is sometimes tied into dominance—there might be issues with the established hierarchy in your home (we will talk about ways to correct this further down). Similarly, issues like food aggression can be triggered by territoriality (if you’re not feeding your dogs far enough apart or separately).
Dominance is somewhat linked to territoriality and is often seen at places like the dog park or when a visiting dog comes into the house with a visiting friend/owner. If your dog is not used to sharing their space with others, he or she might act aggressively towards the visitor.
A dominant dog, too, wants to let other dogs know right away that they are top dog (they will not let another dog jump up on them or try to hump them, nor will they play-bow or roll over on their back to show their belly in a social setting). Dominance can be part of the make up of your dog or be breed-specific (certain breeds like terriers, herding breeds, and so forth can be pretty rigid in play groups versus a labrador, for example).
It’s important to note that if your dog is intact and not spayed or neuter, you will encounter even more problems. It is highly encouraged that you spay and neuter your pet so that you can prevent behavioral issues like aggression in both male and females that gets triggered further into adulthood/with maturity.
7. Protecting the Owner, Family, or Family Pet
Some dogs sense that it is their duty to protect their family (other pets included) from strange dogs and strange people. They may misinterpret a situation like a jogger running by or the other dog behind the fence as an immediate threat to the family. Even at a dog park, for instance, such issues can creep up. You might be petting a friendly dog when your dog comes out of nowhere and gets between you and them dog, growling and snarling. Your pet might even lunge at the visiting dog with no warning.
If your dog is inherently insecure or misinterpreting a situation, they might go on the defense. While dogs make incredible companions and are loyal protectors, they do make mistakes, too. It’s your job to ensure them that everything is okay by way of your body language, tone, and gesturing. We will talk about this further down.
8. Excitability or Curiosity
Some dogs tend to be overly excited or curious, in which case they are unable to handle a certain situation—this can, unfortunately, lead into instances of aggression or worse. For example, your dog might be let off leash in the dog park and go tearing off in all directions. The flood of chemicals released in the brain from the introduction of various stimuli can, in a sense, cause them to “short circuit.”
When dogs are faced with a flood of stimuli, they might act out in ways that seem counter to the situation. If they are excited, their excitement can jump the barrier into aggression. If they are curious about something, they may approach it, only to be triggered. Curiosity-triggered aggression might occur in instances when your dog is meeting another species (like a goat at a farm). Maybe the goat jumps or kicks suddenly . . . your dog could react aggressively to this unpredictability. While sadly, the behavior is mismatched to the circumstance, there are ways to prime your dog for better interactions through controlled introductions. We will talk about this further down.
9. Barriers (Leash or Fence)
Barriers are a huge reason for aggression in dogs. It is not uncommon for dogs to go to war behind a fence. They might actually be great playmates when meeting face-to-face in an open field, but when separated by a fence, all bets are off. In addition, leashes can cause a similar effect. If you’re walking and your dog sees a skateboarder, a jogger, or another dog from across the street, they might have a tendency to lunge to get at that thing.
The leash puts a lot of pressure on the neck region of the dog (one of the most vulnerable areas, the jugular, and an often targeted region when a predator goes for the kill). The pulling on the neck (especially if you don’t have a proper harness) just agitates your dog further. It’s important that you find ways to properly leash-walk your dog, train them through their struggles, or work on a schedule with your neighbor to prevent issues behind the fence.
10. Prey Drive
Unfortunately, some dogs (mixed breeds) and especially purebreds (more predictable), have a high prey drive. If they are of a larger breed, this means they automatically see anything small, fast, and moving (even children or babies) as a target. If your dog chases squirrels or cats, it’s possible that they will also chase small dogs.
If you have a dog that is of a herding breed (cattle dog, healer, Australian Shepherd, and so forth), you really need to watch them with other dogs. High prey drive is hard to train out of dogs, it’s their instinct, and this can cause them to attack other animals in the house (smaller family members like birds, cats, guinea pigs, hamsters) and unfortunately kill them, and it can cause them to attack other dogs in an open-field setting or when off-leash. As an owner, you are responsible for your pet. We will talk about ways to combat high prey drive further down.
11. Issues With Health
Unfortunately, underlying health issues can cause a dog to be aggressive and attack. Certain viruses that affect dogs either from an early age or even into adulthood (if not vaccinated) like distemper, which causes neurological damage, can affect your dog’s perception of the world. Neurological issues can also be caused by medical problems like brain tumors or old age. Neurological issues impact a dog's ability to sense its surroundings. They may interpret a shadow passing over their face as a dog coming towards them, prompting them to attack. In such a case, you should be mindful of your dog’s limitations and avoid triggering or questionable environments.
In addition, older dogs that have osteoarthritis or other injuries or pain, even cognitive decline in general, may act out when they are approached or physically touched. Older dogs that are painful will try to defend themselves against a younger dog that is trying to jump on them (because it hurts to be jumped on!).
If you are considering getting a puppy or adopting another dog for your household and have a senior dog, make sure it’s a good match. Getting a hyperactive dog that loves to jump and tackle is a bad idea and will make your senior dog’s existence difficult.
One of the biggest causes of aggression in dogs is because of the owner. This is an often overlooked issue because people tend to blame the animal first, but it really comes down to nurture over nature in this scenario. Owners who are anxious for whatever reason (maybe you had a bad experience in the past after witnessing a dog fight) or owners who do not have control of their dog, can transmit their anxiety either in body language, vocal tone, posture, and even things like tension on the leash.
When your voice changes, your body language changes, and you pull your dog in close to you, you are indicating to them that there is a threat. It is imperative that you stay calm, cool, and collected, and learn how to work with your dog and dispel your anxious tendencies. This is also true of interactions in the household. We’ll talk about techniques to combat your issues below.
10 Ways to Stop a Dog From Being Aggressive Towards Other Dogs
Combatting issues of aggression in dogs really comes down to the owner: It is your responsibility to control your dog and raise a well-rounded, well-socialized canine. Here is some advice to get you started:
1. Control Your Tendencies
Animals are very sensitive to energy and pick up on communication techniques (body language, tone, scent) that humans are rather oblivious to. It is not uncommon for dogs with overly anxious owners to act out in aggression. An owner who goes out with their dog and carries stress, tension, or fear within them will transfer that to their dog.
You cannot blame your dog for reacting to your needs and the energy that you are transmitting. If you tense up on the leash every time another dog passes or you nervously say “good boy, good boy,” when you anticipate your dog’s negative reaction to another passerby, this doesn’t do any good and is only triggering the aggressive tendencies. Consider learning how to properly work with your dog out in public by enlisting in a class with a reputable dog behaviorist. Focus on managing your anxiety as well.
2. Teach Your Dog “Neutrality”
Teaching your dog to be neutral when a stimulus crosses your path is very important. If you can teach neutrality or desensitize your dog to other dogs walking by on a leash or even passing by your home, you are working towards success. Teaching neutrality also comes from you—you need to pretend like that dog across the street or the mail delivery person is nothing special.
You can start by ignoring and not even looking at or acknowledging common triggers. When you see a dog across the street, don’t even look, just keep your normal pace on leash and have your dog keep stride with you as if you’ve got business to take care of. Remember, lead by example.
3. Learn to Read Your Dog’s Body Language
By understanding your dog and how they communicate via body language, you can set your dog up for success rather than failure. Certain signs trigger your dog’s discomfort, these include: tensing of the body, hair raising on the back, ears and tail erect, growling, or, alternatively, cowering, scooting away, whining, struggling on the leash or trying to escape.
Whether your dog is the dominant type or the submissive type, both ends of the spectrum can lead to aggression. Dominant dogs can act out aggressively or submissive dogs can act out of fear and feeling threatened. When you see that your dog is starting to get uncomfortable, it’s time to remove them from the situation.
4. Use Visual/Physical Barriers and Distractions
In addition to teaching neutrality, using visual or physical barriers and distractions can work wonders when it comes to training your dog to avoid triggers. A visual barrier could mean simply walking on the opposite side of bushes rather than passing another dog nose-to-nose when out on the leash . . . it could also mean that someone in your walking group (or you) stands on the near side to the unfamiliar dog. By keeping your dog on the far side (away from the passing dog), you prevent your dog from crossing over you. This is only recommended if you have good control of your dog on the leash. When using this technique, you can also match your stride to be in front of your dog’s nose so that they have a hard time actually seeing what is passing (i.e. the trigger, be it a dog, jogger, scooter, cat, bicycle, etc.).
Distractions are great, too. Distractions may come in the form of treats (sit, watch, reward with treat) or in the form of a toy or even a noise (like a clicker or whistle of the lips). I’ve seen dogs successfully redirect their attention when their favorite toy is brought out in front of them. Work with the clues you already have about your dog—what makes them tick and what is it exactly that they will work for.
5. Keep Greetings Short and Sweet
Another important tip is to allow your dog to meet and greet other dogs but to keep it short and sweet. As always, you need to take the time and courtesy to ask the other owner if their dog is friendly. (Most owners will say “yes” but that does not mean their dog is always on perfect behavior, always take caution.). Once you get the okay to approach the other dog, keep the nose-to-nose greeting short and sweet.
A simple sniff-sniff and wag is enough time to say “hi” and to keep walking. Anything longer than that can turn into a play session (think play bows and tangled leashes) or might welcome enough time and tension to create an uncomfortable, provoking situation that invites aggression. Even friendly sessions can sour if playing starts and leashes get tangled; tangled leashes are scary for dogs and might provoke one to act out and bite out of fear and not knowing what’s happening (e.g. from getting a leg caught in a harness or leash/getting hurt).
6. Learn to “Read the Room”
Don’t set your dog up for failure and learn your dog’s triggers. Don’t put your dog in weird situations where they are set up to fail. For example, if you have a smaller dog and you throw them in a dog park full of larger dogs and they get cornered in a small space, of course they are going to act out to defend themselves (they are scared!). Luckily, some dog parks are separated by size and allow you to place your dog in the correct area to play with dogs of similar stature or size.
If your dog hates fences or only acts aggressively on a leash, then take them to an off-leash site to let them run and play or reinforce your fence with a solid visual barrier so that your dog cannot access the other dog behind the fence. Fence aggression is often triggered from frustration, too, of not being able to reach the other dog. Perhaps they just need to meet and play it out.
Another common example that results in aggression is releasing your dog into a playgroup or letting your dog play with another one that is poorly matched to their size, stature, or play style. A senior dog, for example, does not want to play with a large, rambunctious labrador puppy (most don’t). A Chihuahua does not want to be the focus of a game of chase in a group of 10 dogs of varying size. If your dog hates cats, don’t walk them by the house with the neighbor’s bold outdoor cats. If your dog hates children on scooters or bicycles, don’t walk them outside during school hours when kids are commuting. Be smart about what situations you put your companion in.
7. Use the Right Leash
If your dog loves to pull and lunge on a leash, invest in a better leash that offers more correction and control. A harness can be good for some dogs (or it can turn them into sled dogs). There are great corrective leashes available that go across the body or attach to the top of the muzzle (check these out). If your dog has a bite record (this is extremely serious), use a soft cloth muzzle when you take them out in public and walk them away from people and children. As always, you need to be able to control your dog. It is up to you as the owner to make sure your dog is safe when out in public.
8. Work With a Canine Behavior Specialist
It is always advised that you work with a good trainer with any type of dog regardless of desirable or undesirable traits. You should have some understanding of canine behavior and proper training techniques as taught by way of an expert. It is never too late to start. This is just an essential part of being a responsible owner. Even experienced dog owners always have more to learn.
When your dog starts to exhibit undesirable behavioral issues, you need to get in touch with a trainer ASAP. Ask your veterinarian for recommendations or do some research yourself. A trained behaviorist should be licensed/credentialed and have clients to show for that and success stories to show for their work. Work with someone who uses positive training methods for correction (rather than negative); scolding your dog, punishing them, or using cruel methods like shock collars will only worsen their behavior and damage your relationship with them.
9. Socialize Early (Puppy Socialization and Training)
This cannot be emphasized enough—early socialization is everything. Unfortunately, some dogs miss the window to enroll in training or puppy socialization class, but you can still start from scratch. Dogs are quite shapeable and even those with negative history or trauma can be rehabilitated if they work with the right person or are taken care of by the right professionals. You can be that person to get your dog into a happy, well-socialized place. It takes a lot of trust and time, but with proper guidance (from a behavior specialist), you can get your dog back on track.
As for most social species, early socialization is crucial. Most puppies learn what to do and what not to do by interacting with their mom and littermates. Unfortunately, some dogs get separated very early on.
Once your puppy is current on the first two rounds of core vaccines, you can start to consider what methods you want to take to get them socialized. Puppy classes are great because they consist of a pretty fair spread across the board (all puppies!) and owners are often obligated to show proof of vaccination. These classes also take place indoors on sanitized surfaces and they are supervised.
10. Focus on the Good
Create happy experiences for your dog. When they greet another dog and act positively rather than negatively, celebrate this with treats or praise. Reinforce good behavior always. If your dog runs out into the backyard along the fence and doesn’t bark or demonstrates good recall, celebrate this as well. A celebration can involve treats, toys, praise (verbal), love (pets), and other kinds of fun. The more positive scenarios you can create for your companion, the better their overall sense of life and life experience will be. Set them up for success and give them everything and more.
What About Dogs Fighting in the Same Household?
When two dogs fight in the same household, this can be an extremely upsetting situation. Most of the time this has to do with resources—they are fighting over territory, people, favorite spaces (beds, crates, couches), toys, and more. It is very important that you do not attempt to reach in between your two dogs if a fight breaks out (you can get injured by doing this). If you need to break up the fight, use objects (brooms, a water hose, if outside), make a lot of noise to disrupt them or surprise them (bang pots and pans), you might even throw a bag of food (bread) on the ground to get them to pull away.
Oftentimes, the fights can be short lived and might just be a quick scuffle (remember, dogs communicate differently from humans). A simple growl-snap is scary but it is also their way of saying “back off” or “leave me alone” (just like how humans posture or throw a punch).
Small Dog vs. Bigger Dog
The most dangerous situation is when the playing field is not fair—smaller dog vs. bigger dog, young dog vs. senior dog. It is up to you to establish boundaries. If your younger dog is beating up on your older dog, stop it (don’t tolerate it). If you dogs fight over a bed or a place on the couch, establish where each dog belongs. You can set up their dog beds in specific regions of the house, or train them to both wait to be invited up on their respective spots on the couch.
In addition, carrying a smaller dog and placing them down on the ground also welcomes aggression—you are enticing the aggressor to go after the small dog by withholding them (physically) and making them interesting.
You might also consider setting up suitable places for your smaller dog to feel safe/secure, like a small, open crate, or even using baby gates that allow a small dog to pass through the bottom/a larger dog to stay on the other side (this gives the small dog the option of escape). You might use such a baby gate to block off sections of the house (thus allowing your small dog to pass through and enjoy one area of the house safely) when times get heated or they need a break. Supervision is also very important.
If they are fighting over food, you should already be feeding them separately. This means making them both sit and wait for their bowl. Feed them in separate rooms. Feed your “alpha” dog (the older dog or the dog that was first in the family) first and then walk your other dog into another room and close a baby gate or door to prevent them from feeling tempted to check up on the other.
If your dogs are fine for a few hours and then erupt in aggression, rotate them in the household—maybe one of your dogs gets supervised outdoor time or goes for a long walk with a family member while the other roams in the house. You might also consider offering time for each dog in regions of the house using doors/shut rooms to keep them separate and to give them a break. Let one dog hangout in a room with a family member (maybe while they work remotely) and let another one free-roam as you cook in the kitchen. You can also experiment with crate time.
Though not necessarily the best option, you can give the aggressor a time-out in the crate. It helps to sensory deprive them (in a kind way) by covering their kennel with a blanket and let them rest/chill out if things are getting too intense. (Important: Do not let your other dog roam around the crate or sit at the front of the crate when you are ready to let the resting dog out; this builds tension and is not fair to either.)
Bring a Certified Behavioral Specialist Into Your Home
Lastly, invite a certified behavioral specialist into your home. They will be able to assess the dynamic and talk about ways you can help reduce the likelihood of a fight between your two dogs with training and some strategic methods. Of course, you might also have to consider the really difficult situation of rehoming one of your pets if the fights are violent, cause bleeding, injury, or put one of your dogs at risk of death.
Dog fights are no joke and dogs can kill each other in the same household and injure their family members. It’s heartbreaking, but if you can find a family friend or know of someone you trust to take in one of your pets, this is the best outcome (you can still visit them); also consider breed-specific rescues and surrenders at no-kill shelters. This should be the absolute last choice after talking to your veterinarian and spending a considerable amount of time with a behavioral specialist. Having children or other small pets in the house that are at risk of being injured might also influence this decision.
All in all, your pet’s wellness is what you make it. Be smart, think of ways you can be proactive in helping your dog, and also consider the various resources we have discussed above.
This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.
© 2021 Laynie H
Laynie H (author) from Bend, Oregon on January 13, 2021:
Hi Peggy, thanks for the read. I grew up with an aggressive dog (unfortunately), we got her as a rescued puppy. She had a high prey drive. I learned a lot from her considering we lived with a cat and she didn't not get along with other dogs.
Peggy Woods from Houston, Texas on January 13, 2021:
You have listed all kinds of reasons why dogs might react aggressively and also things to do about it. This is an informative article. Thanks!